(i)polyrev

ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton

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Review of Polymers

ver. 1


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Overview• What is a polymer?• Why are polymers good?• Types / examples • Crystallinity• Melting properties• Heat transfer• Fluids• Behavior during

processing


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Just one word: plastic

• The Graduate: 1967


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Polymer production

• 107 billion pounds produced in US and Canada in 2003– volume = 44 million m3

• 217 billion pounds of steel produced in US in 2001– volume = 12.5 million m3


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Polymers

• poly = many• meros = units

• long-chain hydrocarbons– 1,000 - 10,000 units long– 104 - 106 gm/gm-mole


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Why are polymers good?• Light• Corrosion resistant• Strong• Easily formed into complex, 3D shapes

– no further machining necessary• Good filters

– water / gas - permeable / impermeable• reverse osmosis• oxygenators


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Types of polymers

• Thermoplastics– can be melted and solidified repeatedly

• Thermosets– react to polymerize during forming– cross-linked networks– can’t be remelted– decompose with too much heat


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Types of polymers

• Elastomers– large, recoverable, elastic deformations– soft– low glass transition temperatures– partially cross-linked networks– can be thermoset or thermoplastic


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Bakelite• Leo Baekeland

– 1863–1944– first synthetic polymer

(1907)– made from phenol and

formaldehyde


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Polyethylene (PE)

• trash bags, electrical insulation

• thermoplastic


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Polypropylene (PP)

• margarine tubs, food containers

• thermoplastic


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Polystyrene (PS)

• coffee cups (styrofoam)

• clear plastic boxes• thermoplastic


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Polyvinylchloride (PVC)

• credit cards• pipes• thermoplastic


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Polycarbonate (PC)

• Lexan• thermoplastic


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Polymethylmethacrylate (PMMA)

• Lucite, plexiglas• thermoplastic


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Polytetrafluroethylene (PTFE)

• Teflon• bearings• coatings• thermoplastic


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Polyester (PET)

• bottles• carpets• thermoplastic


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Epoxy

• adhesive• composite matrix• thermoset


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Rubber – vulcanization (1844)

• elastomer• thermoset

Charles Goodyear1800-1860

VulcanRoman god of fire


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Bonding

• Leads to all mechanical properties• Primary

– covalent (C-C, C-O, C-H, C-N)– along chain, interchain

• Secondary– van der Waals– hydrogen– ionic– interchain


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Bonding

• Thermoplastics– covalent along chain– secondary between chains– 2D structure

• Thermosets– covalent along and between

(cross link) chains– 3D network


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Bonding

• Elastomers– partially cross-linked– 2.5 D network


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Crystallinity

• Short range order (1,000s of Å)• Amorphous

– PS, PC• bulky side groups prevent packing

• Semi-crystalline– PE, PP

• small or no side groups allow packing


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Crystallinity• Tightly packed• Rigid• Large secondary bonds

crystal region

amorphousregion


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Crystallinity• Spherulites (PP)

• Platelets (PE)


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Effects of crystallinity

• Increased stiffness– matrix reinforcement

• Increased solvent resistance– large secondary bonds prevent solvent

molecules from entering• Crystallinity can go from 0 to 90+%


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Melting properties

mechanicalproperty

temperature

Tg Tm

amorphous

semi-crystalline

glassyrubbery


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Transitions

Material Tg (oC) Tm (oC)

PE -120 137

PVC 87 212

PP -18, -10 176

PS 100 none


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Pressure – Volume – Temperature (pvT) diagram


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Polycarbonate pvT diagram


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Viscoelastic Behavior

• Fast loading or cold = acts like elastic• Slow loading or hot = acts like a viscous

fluid• Example: Silly Putty


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Old Glass Window


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Behavior

• Polymers do not follow a linear stress-strain rate curve

non-Newtonian behavior

• At high stress, μ appears to drop


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Power-law behavior -shear thinning

100

1000

10000

100000

1000000

0.001 0.01 0.1 1 10 100

log μ

)log(γ&

( )nγμ &=


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Elastic die swell

• Extrudate can swell 2-3 times tube diameter at high strain rate (~1/sec)


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Release of elastic energy

• In tube, molecules are stretched out

• On release, molecules re-coil to minimum energy state


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1D Conduction Heat Transfery

x

2l

2

2

xT

tT

∂∂

=∂∂ α

T = temperaturet = timeα = thermal diffusivity


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Example 1-1

• PC (α = 10-3 cm2/s)• τ(1/8”) =

(0.15)2/10-3 = 22 s• τ(1/4”) = (0.3)2/10-3

= 90 s

• Al (α = 0.91 cm2/s)• τ(1/8”) =

(0.15)2/0.91 = 0.02 s• τ(1/4”) = (0.3)2/0.91

= 0.1 s


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Fluids

• Polymers are very viscous• μ = 102 - 104 Pa-s• 105 -104 x water

( ) ( ) ( )( )viscosity

diametervelocitydensity

Re

∗∗=

=μρVd


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Example 2-1

• PE melt at 200-300oC• μ = 5 x 105 g/cm-s• For creeping flow, Re = 1, 1 mm tube

• so v = 5 x 106 cm/s (quite fast)– Mach 150

( ) ( ) ( )( )scmg −

∗∗=

/10 x 5cm 0.1velocitygm/cm 1Re 5

3


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Example 2-2

• Water at 200-300oC• μ = 2.5 x 10-2 g/cm-s• For creeping flow, Re = 1, 1 mm tube

• so v = 0.25 cm/s (a bit slower)

( ) ( ) ( )( )scmg −

∗∗=

/10 x 2.5cm 0.1velocitygm/cm 1Re 2-

3


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Summary

• Polymers• Properties• Heat transfer• Fluids• Behavior


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(i)polyrev

Documents

manufacturing processes

plexiglas thermoplasticme

polymers good

crosslinked networks

chain hydrocarbons

synthetic polymer

pounds of steel

interchain secondary